Changes Of Neuropathology In The Retinas Of Experimental Diabetic Rats In Early Stage

In traditional opinion, abnormalities in retinal vascular system are the primary cause in the occurrence of DR. The dysfunction of retinal microvessels induced by diabetes caused the extensive ischemia and hypoxia in the retinas. That led the edema and angiogenesis which resulted in vision loss and blindness. Thereby, the diagnosis, treatment and much of the research effort have been focused on vascular changes.Animal models are usually used to provide methods of research on the pathogenesis of diseases in human being. In rodent models of diabetes, vascular changes similar to those seen in human patients have been demonstrated, but this visual vascular changes are observed several months (at least three months to six months) following the onset of diabetes. In previous researches, most of them focused on the pathology after the appearance of microangiopathy in diabetic animals. Nevertheless, in recent years agrowing number of proofs support the retinal neurons have begun to show pathological changes in early stage after the onset of diabetes, and the opinion is suspected that the dysfunction of microcirculation happen first of all and then leads the injury of nervous tissue. Therefore, the research on the pathological characters of neural tissue in the retinas is very important to reveal the pathogenesis of DR.Objective: To observe that the pathological changes of the neurons in the retinae before the present of visual microangiopathy and those in the hippocampus and cortex. It was to explore the effects on the neurons induced by diabetes in the early stage.Methods: 1. We produced diabetic rat models induced by streptozotocin (STZ) and measured the basic physiological indices in diabetic and control rats. 2. The Electroretinograms (ERG) were recorded in diabetic and control rats. 3. The retinas and brains were obtained in the end of experimental duration (6 week). 4. The techniques of general hematoxylin-eosin staining, immunohistochemistry staining and transmitting electron microscopy were used to observe the characteristic changes of neural tissue in the retinas. 5. The techniques of above were also used to observe the characteristic changes of neural tissue in the hippocampus and cortex.Results: 1. A reliable method for the diabetic rat models: It suggested that the method of intraperitoneal injection of STZ was convenient. The successful ratio of diabetic rat models was high (85%) and the regression ratio (5.6%) was low. The each rat in control group drank about 40 ml water every day and body mass of it increased fast with its week age. The each rat in diabetic group drank about 400 ml water every day and body mass of it did not grow with its week age. Blood glucose in control rats was between2.8⁷.5mmol/L and it in diabetic rats was above the requirement of models. Urine glucose in control rats was negative (-) at each time, and it in diabetic rats was strong positive (++++).2. Visual electrophysiology: According to standard program recommended by International Society for Clinical Visual Electrophysiology, we recorded the rod-response, max-response, oscillatory potentials (OPs), photopic electroretinograph (phot-ERG) and 20 Hz flicker response at Owk, lwk, 2wk and 5wk in diabetic rats induced by streptozotocin (STZ) and age-matched control ones. The results indicated that before and at the first week after onset of diabetes, the ERG of diabetic rats did not differ significantly from that of control ones; at the second and fifth week, the implicit times of b wave of rod-response, b wave of max-response, O₂ wave of OPs and b wave of phot-ERG of diabetic rats were respectively prolonged significantly compared to those of control ones; but the amplitudes of ERG of diabetic rats were not different significantly at all times from those of control ones.3. Changes of histopathology in the retinas: (1) The retinal constitutions in sections for general hematoxylin-eosin staining in diabetic rats were not different compared with those in control ones in light microscopy. There are kinds of cell layers in order from the vitrea to scleral sides and normal shape in nuclei. (2) The expressions of GFAP in astrocytes in diabetic rats were much less than those in control ones, but the expressions of Vimentin and S100 in muller cells in diabetic rats did not differ from those in control ones. (3) The retinal electron microphotographs in diabetic rats showed degenerative changes in the ganglion cells, photoreceptor cells and pigment epitheliums.4. Changes of histopathology in the hippocampus and cortex: (1) The neurons in sections of the hippocampus and cortex for general hematoxylin-eosin staining in diabetic rats were not different compared with those in control ones in light microscopy. The forms of nerve cells were normal. (2) The expressions of GFAP and S100 in nerve cells in the hippocampus and cortex in diabetic rats were much more than those in control ones, but the expressions of Bcl-2 in neural cells in diabetic rats were less than those in control ones. (3) The electron microphotographs in the hippocampus and cortex in diabetic rats showed normal vascular cells and degenerative changes in the nerve cells.Conclusion: Collectively our work has demonstrated that retinal neurons had degenerated before the visual vascular pathology appeared. The astrocytes and ganglion cells near the inner blood-retina-barrier and pigment epithelial cells and photoreceptor cells near the outer blood-retina-barrier were more sensitive to lesion induced by high blood glucose than other neural cells. In the same time we also found that the pathological changes in neural cells were very slight so that they could be distinguished by the advanced experimental methods.By observing the pathological changes in the hippocampus and cortex, it was found that the pathological characters in neural cells in retinas were different from those in brain tissue in spite of the similar constitution in retina and brain tissue. But the experimental results in both of brains and retinas suggested that neural cells had appeared obvious pathological changes in early stage of diabetes.We concluded that the neural and vascular tissues in the retinas were simultaneously damaged when diabetes happened. It was not true that vascular tissue was injured firstly and ischemia and hypoxia induced by dysfunction of...